This invention relates in general to an electromagnetic valve for controlling fluid flow, and more particularly a fuel injector valve used in an internal combustion engine.
In a usual electromagnetic valve for fluid flow control, a movable valve member is biased by a spring in the direction to perform valve closing, so that the valve member is biased toward a valve seat by the force of the spring to maintain the valve closing state when electric current is not passed through an electromagnetic coil. Such an electromagnetic valve has encountered the following problems: the response of valve opening is not good since the valve member is always biased by the spring. Additionally, the spring itself also vibrates during operation and accordingly it is impossible to obtain uniformity in fluid flow characteristics.
In order to solve these problems, a new type of electromagnetic valve has been proposed, in which a valve member is biased onto a valve seat to perform valve closing, without using a spring, by the action of pressure differential between the upstream and downstream sides of the valve member.
However, with this electromagnetic valve arranged to perform its closing action by only the pressure differential, various disadvantages have arisen. For example, where the electromagnetic valve is a fuel injector valve and it is disposed lateral relative to the engine, when the fuel pressure within the valve lowers and a biasing force to the valve member is decreased, the valve member is moved downward to separate from a valve seat by the action of gravity and accordingly the fuel within the electromagnetic valve is liable to leak through a clearance formed between the valve member and the valve seat. As such, during engine stoppage in which the fuel pressure within the electromagnetic valve decreases, fuel staying in a fuel piping system leaks out of the electromagnetic valve and into an intake conduit into which the fuel injector valve projects to inject fuel, the intake conduit leading to the engine. As a result, the air-fuel mixture supplied to the engine is liable to become too rich to re-start the engine, which renders the re-starting of the engine difficult.